The present invention relates to a multi-stage capacity-controlled scroll compressor which enables partial load operation in lower capacity regions.
Conventionally, as a scroll compressor which enables partial load operation with a bypass hole formed in a scroll, there has been available one as shown in FIG. 8 and FIG. 9, which is a sectional view taken along the line Xxe2x80x94X of FIG. 8 (Japanese Patent Laid-Open Publication HEI 9-170573). This scroll compressor is an asymmetrical spiral-type scroll compressor in which a scrolling end of a first scroll 1 is xcfx80 (rad) longer in involute angle than a scrolling end of a second scroll 2. A first fluid working chamber A defined by an inner surface of the first scroll 1 and an outer surface of the second scroll 2, and a second fluid working chamber B defined by an outer surface of the first scroll 1 and an inner surface of the second scroll 2 are alternately opened and closed to a single low-pressure port 3. A common bypass hole 4 common to the first fluid working chamber A and the second fluid working chamber B is provided at a point j which is a point about one-scroll inwardly unwound from an outermost side contact point E of the second scroll 2 with the first scroll 1.
Then, a valve hole 5 communicating with the common bypass hole 4 is formed in the first scroll 1, and a bypass passage 6 communicating with the low-pressure port 3 is formed in a side portion of the valve hole 5. In the valve hole 5, a stepped cylindrical bypass valve 7 for opening and closing the common bypass hole 4 is internally fitted so as to be slidable. Also, a coil spring 8 is engaged with the stepped portion of the bypass valve 7, and an upper portion of the bypass valve 7 is closed by a lid member 9 and thereby partitioned from a discharge dome 10 to define an operating-pressure chamber 11. In addition, an operating-pressure line 15 communicated selectively with a low-pressure line 13 or a high-pressure line 14 by a solenoid valve 12 is connected to the operating-pressure chamber 11 via a joint tube 16. Reference numeral 17 denotes a capillary tube for preventing shortcircuit between the high-pressure line 14 and the low-pressure line 13, numeral 18 denotes a casing, and numeral 19 denotes a high-pressure port.
As described above, the common bypass hole 4 is formed at the point j, which is a point about one-round inwardly unwound from the outermost side contact point E of the second scroll 2 with the first scroll 1. Therefore, when high-pressure gas is supplied to the operating-pressure chamber 11 of the bypass valve 7 by closing the solenoid valve 12 and then the bypass valve 7 is closed, discharge capacity becomes the full capacity (100%). On the other hand, when low-pressure gas is supplied to the operating-pressure chamber 11 of the bypass valve 7 by opening the solenoid valve 12 and then the bypass valve 7 is opened, the discharge capacity becomes about 60% of the full capacity because the position of the common bypass hole 4 serves as a compression start point. In this way, the discharge capacity of the scroll compressor is switched between 100% and 60%.
In addition, it is also possible to provide two common bypass holes at a position which is about xc2xe-round inwardly unwound from the outermost side contact point E of the second scroll 2 with the first scroll 1, and another position which is a one-round inwardly unwound therefrom, so that three discharge capacities, 100%, 70% and 60%, can be obtained.
However, the above multi-stage capacity-controlled scroll compressor of the prior art has the following problems. First, because its volume ratio Vr considerably lowers during a 50% or lower partial load operation, there is a problem that the operational range is limited.
For example, in the case where the intrinsic volume ratio Vr of the first and second scrolls 1, 2 is Vr =2.3, since the volume ratio Vr needs to be not less than xe2x80x9c1xe2x80x9d even with a partial load as a compressor, the critical partial load ratio is 1/2.3=0.44, that is, a 44% operation is a limit. Indeed increasing the intrinsic volume ratio Vr causes the critical partial load ratio to lower so that a 50% or lower partial load operation is enabled, but the efficiency at the full load would be lowered in that case, conversely, so that increasing the intrinsic volume ratio Vr could not be adopted. However, in a multi-type air conditioner in which one outdoor unit serves for a plurality of indoor units, a 20% to 30% load operation is necessarily required so that when the conventional multi-stage capacity-controlled scroll compressor is applied to this multi-type air conditioner, there would arise problems that the compressor runs and stops frequently, or that optimum conditions for air-conditioning cannot be set.
Also, as a load-controlled scroll compressor, there has been available a method using inverter control of motors besides the above scroll compressor. In this case, unfortunately, an inverter circuit is required, leading to a great cost increase. Particularly in large-size inverters, there is a further problem that harmonics would be generated. There is still another problem of lubrication failure during the inverter operation, which causes a reliability deterioration of the compressor as yet another problem.
Furthermore, when a multiplicity of common bypass holes are formed with an aim of a low partial load operation of 50% or lower as described above, machinability or assemblability deterioration maybe incurred or rigidity may deteriorate because of the common bypass holes formed at central portions of the first and second scrolls. Besides, because the gas load within the scrolls of the first and second scrolls decrease to a large extent, the gas load and the centrifugal load of the movable-side second scroll are unbalanced, so that malfunction such as lubrication failures at a pin bearing (not shown) or the like may occur, or that the second scroll. may be turned over, as further problems.
Therefore, an object of the present invention is to provide a multi-stage capacity-controlled scroll compressor which is capable of changing 50% or lower partial load operation in multiple stages and which is low in price and high in reliability.
In order to achieve the aforementioned object, there is provided a multi-stage capacity-controlled scroll compressor comprising:
a first bypass passage formed at a specified position in a compression chamber and serving for returning compressed gas present in a fluid working chamber to a suction port;
first opening/closing means for opening and closing the first bypass passage;
a second bypass passage for communicating discharge side and suction side with each other;
second opening/closing means for opening and closing the second bypass passage and for, with the second bypass passage opened, letting high-pressure gas on the discharge side escape to the suction side by a specified quantity.
With this constitution, the second opening/closing means opens and closes the second bypass passage, by which the load of the compressor can be switched between 100% and a first specified %. On the other hand, the first opening/closing means opens and closes the first bypass passage, by which the discharge capacity of the compressor can be switched between 100% and a second specified %. Accordingly, in combinations of the opening and closing operations of the first opening/closing means and the opening and closing operations of the second opening/closing means, effective load of the compressor can be changed over in four stages. In this case, the discharge capacity of the compressor can be changed over only to the second specified % by the first opening/closing means. Therefore, if the fixed volume ratio for the compressor and the second specified % are so set that the volume ratio at which the discharge capacity of the compressor becomes the second specified % becomes 1 or more, then the volume ratio can be maintained 1 or more even when the effective load of the compressor becomes a minimum, so that high-reliability multi-stage load control can be achieved.
In an embodiment of the present invention, a first scroll and a second scroll of which the compression chamber is formed show asymmetrical spiral shapes, respectively, that a spiral end of one scroll is 180 degree longer in involute angle than a spiral end of the other scroll.
With this constitution, the first fluid working chamber defined by the inner surface of the first scroll and the outer surface of the second scroll and the second fluid working chamber defined by the outer surface of the first scroll and the inner surface of the second scroll are formed alternately at positions on the same first bypass passage. Accordingly, the high-pressure gas in the fluid working chambers is returned from the only one first bypass passage to the suction port.
In an embodiment of the present invention, the second bypass passage is provided outside a body of the compressor.
With this constitution, the second bypass passage and the second opening/closing means do not need to be formed within the compressor body, and may be formed between discharge line and suction line. Accordingly, the multi-stage capacity-controlled scroll compressor is produced with low price.
In an embodiment of the present invention, the second bypass passage and the second opening/closing means are provided each in a plural number.
With this constitution, the second bypass passage and the second opening/closing means are provided in pluralities. Accordingly, in combinations of the opening and closing operations of the second opening/closing means and the opening and closing operations of the first opening/closing means, 8 or more stages of multi-stage load control is achieved.
In an embodiment of the present invention, the second opening/closing means for opening and closing the second bypass passage is a motor-operated valve which is controllable to any arbitrary degree of openness.
With this constitution, since the opening of the second bypass passage is set to an arbitrary degree of openness, load of the compressor can be switched between 100% and any arbitrary %. Accordingly, in combinations of the opening and closing operations of the first opening/closing means and the opening and closing operations of the second opening/closing means, effective load of the compressor can be changed over in an arbitrary multiplicity of stages.
In an embodiment of the present invention, the second opening/closing means operates on a differential pressure between a pilot pressure and a pressure on the suction side or a pressure on the discharge side.
With this constitution, the control system for the second opening/closing means can be implemented with simplicity, so that the multi-stage capacity-controlled scroll compressor is produced with low price.
In an embodiment of the present invention, the multi-stage capacity-controlled scroll compressor, further comprises a liquid injection tube for cooling a low-pressure chamber communicating with the suction port.
With this constitution, the low-pressure chamber and the driving motor are cooled by cooling liquid injected from the liquid injection tube. Thus, temperature increase of the low-pressure chamber due to the return of the high-pressure gas in the compression chamber to the suction port is prevented, making it possible to lower the temperature of the discharged gas and the motor.
In an embodiment of the present invention, the first opening/closing means and the second opening/closing means operate on a pilot pressure, and
a pilot port of the first opening/closing means and a pilot port of the second opening/closing means are connected to their corresponding pilot lines, respectively, via one joint fitting provided at an upper center of the compressor body.
With this constitution, the joint fitting that connects the pilot ports of the first and second opening/closing means and their respective pilot lines to each other need to be provided only one in number at an upper center of the compressor, so that the port and line connection can be taken out from one place, the casing top center. Therefore, as compared with the case where the port and line connection is taken out from two decentered places of the casing top, in which case elliptical welding with the operating tube needs to be provided at two places, the welding work between the casing top and the operating tube can be achieved with simplicity, so that the man-hours for assembly is reduced, thus allowing a further cost reduction.
In an embodiment of the present invention, a multi-stage capacity-controlled scroll compressor comprises:
the multi-stage capacity-controlled scroll compressor as defined in Claim 1, and
a standard scroll compressor of a specified discharge capacity, wherein
the multi-stage capacity-controlled scroll compressor and the standard scroll compressor are connected to each other in parallel.
With this constitution, a twin multi-stage capacity-controlled scroll compressor is made up of a multi-stage capacity-controlled scroll compressor and a standard scroll compressor. Accordingly, in a combination of switching to two load states of unload and full load with the standard scroll compressor and n-stage load switching with the multi-stage capacity-controlled scroll compressor, load can be changed over in 2xc3x97n stages. Thus, load control can be achieved in even further multiple stages.
In an embodiment of the present invention, the first opening/closing means operates on a pilot pressure, and
a pilot port of the first opening/closing means and joint fittings for connecting a pilot line to the pilot port are connected to each other by screws.
With this constitution, the pilot port of the first opening/closing means and the joint fitting are securely connected to each other by a taper screw. Accordingly, a fitting structure which is highly resistant to variations of the joint fitting and high in leakage resistance and thermal resistance can be realized.